Microwave imaging technology is attractive as an alternative solution for tumor detection, and particularly, for breast cancer detection. Microwave imaging technology is lower-cost and shorter operation time as compared to magnetic resonance imaging (“MRI”) and is less invasive than X-ray.
However, a problem associated with microwave imaging is the low contrast condition for the detection of a malignant tumor. Recent studies have indicated that nearly all breast cancers originate in the glandular tissues of the breast. The dielectric property differences between malignant tissues and glandular tissue is generally not more than 10%. With this slight difference in dielectric properties, the expected reflected/scattered signal from the malignant tumor is very weak. One the other hand, the received signals due to skin backscatter and coupling of the transmitting and receiving antenna (“Tx” and “Rx,” respectively) are comparatively much stronger. Therefore, the desired signal from the tumor is typically immersed in various noise signals.
Conventional methods for overcoming the desired signal to noise ratio have included various calibration and contrast agents. In calibrating the signal, generally the signal acquired from a known, non-tumor region of the breast tissue is subtracted from the signal acquired from the tumor containing region. While this method has been useful in eliminating noise, the method is not practical for real clinical diagnosis since the reference signal is not generally available. Contrast agents, such as golden nano-particles or carbon nano-tubes have been considered; however, some patients may not accept any agent injections.
Therefore, there continues to be a need for signal processing methods that improve the sensitivity of tumor detection by microwave imaging technologies.